There exist numerous configurations for aircraft fuselage doors. The embodiments disclosed herein are especially useful for in combination with so-called aircraft “plug-in” doors. For this type of door to open, it must necessarily move upwardly guided by a rail system. Taking into account the weight of the door, some form of a counterbalancing system is necessary in order to assist the opening and closing operations of a plug-in door. Of the possible counterbalance systems typically available, for example, electric, hydraulic or mechanical systems, the mechanical counterbalance systems possess the lowest cost, weight and complexity.
Mechanical systems currently found are used to provide some or nearly all of the energy needed to lift the door by means of helical torsion springs, made of metal or composite material (see U.S. Pat. Nos. 5,735,020, 4,047,441 and 3,585,757, the entire content of each being expressly incorporated hereinto be reference), or also through helical compression springs (see U.S. Pat. No. 9,033,277, the entire content of which is expressly incorporated hereinto by reference), which uses a compression spring cartridge for counterbalancing the door. However, in all options found, none proposes the use of a torsion bar spring to store energy. In addition, for those proposals which include integrated helical torsion springs (i.e., U.S. Pat. Nos. 5,735,020, 4,047,441 and 3,585,757), the volume of the systems occupy a significant internal space of the aircraft. Moreover, one can infer that the reel and support for these helical torsion springs have a significant weight.
What has been needed in the art, therefore is a counterbalance mechanism for upwardly opening aircraft “plug-in” doors that is of reduced weight and volume so as to be useable in aircraft with smaller available internal space. It is towards fulfilling such a need that the embodiments disclosed herein are directed.